This book, now declassified by the U.S. Government, contains heretofore unpublished methods for solving transposition cipher systems. The solution of grille systems, combined substitution-transposition systems, the ADFGVX System, and the bifid fractionating systems are described in detail. This is an advanced text written in clear terms for the serious cryptanalyst. Analytical key and index are included. Important information not found elsewhere is contained in this book.